[Pdns-users] Spikey response times in powerdns recursor

bert hubert bert.hubert at netherlabs.nl
Wed Mar 17 11:00:35 UTC 2010

On Wed, Mar 17, 2010 at 10:43:19AM +0000, Simon Bedford wrote:
> We have been running  recursor as a caching name server for a number
> of months having moved from unbound, since this time we see good, in
> fact quick DNS response time but then when running and .2
> and also 3.2.1 we see random spikes up to 2 seconds for the response
> times often at the quietest of times for the name servers.

Versions below 3.2 can indeed sometimes show prolonged delays when running
with large caches. This issue is solved in 3.2.

> I had put this down to 3.1 version after reaading the changelog and
> bugs fixed in 3.2 but having upgraded we still see the same spiking,
> this time more frequent over night but not quite as severe as they
> were.

As discussed off-list, you see these spikes for a number of domain names, at
least one of which has a short lived TTL and an unresponsive authoritative

Mar 17 11:57:02 [5] bbc.co.uk.: Resolved 'bbc.co.uk.' NS ns1.bbc.co.uk. to:
Mar 17 11:57:02 [5] bbc.co.uk.: Trying IP, asking 'bbc.co.uk.|A'
Mar 17 11:57:04 [5] bbc.co.uk.: timeout resolving

bbc.co.uk has a 300 second ttl, and thus expires frequently.

> I realise that outside lookups will influence the results but its
> weird that when at their busiest they are more responsive than when
> its quiet and also have most of the unusual behaviour at that time.

When servers are busy, your monitoring system is unlikely to encounter
expired TTLs. This is why a busy server in fact provides superior service
compared to an idle one.

> Recursor performance graphing and dnsscope stats look OK although
> the average time to respon goes up by 100% overnight, see sample
> stats below from overnight/this morning :-

This matches the expectations.


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